[PATCH] D62294: [DAGCombine] (x - C) - y -> (x - y) - C fold

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri updated this revision to Diff 201702.
lebedev.ri added a comment.

Rebased, NFC.


Repository:
  rL LLVM

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D62294/new/

https://reviews.llvm.org/D62294

Files:
  lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  test/CodeGen/AArch64/sink-addsub-of-const.ll
  test/CodeGen/X86/sink-addsub-of-const.ll


Index: test/CodeGen/X86/sink-addsub-of-const.ll
===================================================================
--- test/CodeGen/X86/sink-addsub-of-const.ll
+++ test/CodeGen/X86/sink-addsub-of-const.ll
@@ -460,15 +460,15 @@
 ; X32-LABEL: vec_sink_sub_of_const_to_sub:
 ; X32:       # %bb.0:
 ; X32-NEXT:    psubd %xmm1, %xmm0
-; X32-NEXT:    psubd {{\.LCPI.*}}, %xmm0
 ; X32-NEXT:    psubd %xmm2, %xmm0
+; X32-NEXT:    psubd {{\.LCPI.*}}, %xmm0
 ; X32-NEXT:    retl
 ;
 ; X64-LABEL: vec_sink_sub_of_const_to_sub:
 ; X64:       # %bb.0:
 ; X64-NEXT:    psubd %xmm1, %xmm0
-; X64-NEXT:    psubd {{.*}}(%rip), %xmm0
 ; X64-NEXT:    psubd %xmm2, %xmm0
+; X64-NEXT:    psubd {{.*}}(%rip), %xmm0
 ; X64-NEXT:    retq
   %t0 = sub <4 x i32> %a, %b
   %t1 = sub <4 x i32> %t0, <i32 42, i32 24, i32 undef, i32 46>
Index: test/CodeGen/AArch64/sink-addsub-of-const.ll
===================================================================
--- test/CodeGen/AArch64/sink-addsub-of-const.ll
+++ test/CodeGen/AArch64/sink-addsub-of-const.ll
@@ -314,8 +314,8 @@
 ; CHECK-NEXT:    adrp x8, .LCPI20_0
 ; CHECK-NEXT:    ldr q3, [x8, :lo12:.LCPI20_0]
 ; CHECK-NEXT:    sub v0.4s, v0.4s, v1.4s
-; CHECK-NEXT:    sub v0.4s, v0.4s, v3.4s
 ; CHECK-NEXT:    sub v0.4s, v0.4s, v2.4s
+; CHECK-NEXT:    sub v0.4s, v0.4s, v3.4s
 ; CHECK-NEXT:    ret
   %t0 = sub <4 x i32> %a, %b
   %t1 = sub <4 x i32> %t0, <i32 42, i32 24, i32 undef, i32 46>
Index: lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -2957,6 +2957,13 @@
     SDValue Sub = DAG.getNode(ISD::SUB, DL, VT, N0, N1.getOperand(0));
     return DAG.getNode(ISD::SUB, DL, VT, Sub, N1.getOperand(1));
   }
+  // (x - C) - y  ->  (x - y) - C
+  // This is necessary because SUB(X,C) -> ADD(X,-C) doesn't work for vectors.
+  if (N0.hasOneUse() && N0.getOpcode() == ISD::SUB &&
+      isConstantOrConstantVector(N0.getOperand(1))) {
+    SDValue Sub = DAG.getNode(ISD::SUB, DL, VT, N0.getOperand(0), N1);
+    return DAG.getNode(ISD::SUB, DL, VT, Sub, N0.getOperand(1));
+  }
 
   // If the target's bool is represented as 0/-1, prefer to make this 'add 0/-1'
   // rather than 'sub 0/1' (the sext should get folded).


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